The Premier League veteran sees Mahrez as one of the competition's biggest luxuries.
"He's probably overachieved on what people thought he had in his locker, but Barcelona have come in for a player who has done it for six months - it just shows what quality he's got," Sinclair said.
The former West Ham United winger's claims about Barcelona's interest were reported last week by ESPN FC, whereby the Catalans were rumoured to be thinking of Mahrez as a replacement for the departed Pedro.
Building on his assessment of the 24-year-old, Sinclair also added: "He's probably one of the most exciting players I've seen in recent years in the Premier League."
The Algerian international has been in stunning form for Leicester this season, and Sinclair isn't the first, nor will he be the last to hand the midfielder some rave reviews for his performances.
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Largely in part to Mahrez's contributions, Leicester currently sit in second place in the Premier League; trailing only title favourites Manchester City, who were also victorious again this past weekend.
As well as their standing, Claudio Ranieri's men are the only team able to match the league leaders in terms of goals scored (11), as well as being the only side to remain unbeaten after five league fixtures.
Up next for the Foxes is a trip to face Stoke City, who are just one of three Premier League teams yet to record a victory in the new campaign.